1. Field of the Invention
The present invention relates to an addition-curable type silicone rubber composition, and mole particularly to a silicone rubber composition having excellent durability in repeated mold release.
2. Description of the Prior Art
Silicone rubber compositions, due to their excellent mold release properties, chemical resistance, heat resistance and curability, are widely used as, for instance, materials for rubber mold for molding resins such as urethane, epoxy, polyester and vinyl chloride resins and so-called pattern-making silicone rubber mold materials. The silicone rubber compositions are used also as a rubber material for fixing rolls in dry-type copying machine.
In recent years, however, the requirements for durability in repeated mold release have grown to such a level that none of the conventional silicone rubber compositions can meet the requirements satisfactorily. Namely, when a silicone rubber mold according to the prior art is subjected to repeated molding and demolding, the mold surfaces are deteriorated as the repetition number increases; consequently, for example, the resin moldings obtained will have unsatisfactory surface gloss. Therefore, there is a request for a silicone rubber mold material which enables stable production of molded articles of constant quality even when the molding and demolding cycle is repeated a large number of times, that is, a silicone rubber mold material which has excellent durability in repeated mold release.
In order to improve the durability of silicone rubber mold materials in repeated mold release, the use of an organopolysiloxane having a fluorine atom in its molecule has been proposed. However, this is often accompanied by degradation of rubber properties such as water repellency, oil repellency, curability, heat resistance, etc., and no satisfactory improvement has been obtained.